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Porous aromatic framework
A porous aromatic framework (PAF) is a porous organic polymer built from rigid aromatic units linked by carbon–carbon bonds, giving high surface areas and strong chemical stability.
Porous coordination cages
Porous coordination cages, also known as metal-organic cages or metal-organic polyhedra, are discrete molecular containers with permanent cavities, first reported by Makoto Fujita in 1990.
Porous ionic liquids for CO2 capture
Porous ionic liquids for CO2 capture are sorbent materials combining an ionic liquid with permanent porosity, so the flowing liquid contains permanent cavities that take up carbon dioxide.
Porous liquid
A porous liquid is a liquid with permanent porosity, proposed in 2007 and first realized in 2015 at Queen's University Belfast and the University of Liverpool.
Porous media model
A porous media model is a continuum approach representing fluid flow and solute transport through soils and rocks using averaged parameters like porosity and permeability.
Porous medium equation
The porous medium equation is a nonlinear degenerate parabolic equation, a modification of the heat equation that models gas flow in porous media with finite propagation speed.
Porous organic cages
A porous organic cage (POC) is a soluble cage-shaped organic molecule with an internal cavity; packed crystals form porous molecular solids used for gas separation.
Porous spin-crossover frameworks
Porous spin-crossover frameworks are metal-organic frameworks, typically Hofmann-type iron(II) compounds, whose spin-state switching changes magnetism and color and couples to guest uptake in the pores.
Porphyrin
Porphyrin (porphine, C20H14N4): aromatic tetrapyrrole macrocycle of four pyrrole rings joined by methine bridges; parent of heme, chlorophyll, and vitamin B12-type cofactors, used in photodynamic therapy.
Porphyrin-based metal–organic framework
A porphyrin-based metal–organic framework, also called a porphyrinic MOF or PMOF, is a crystalline porous solid using porphyrin linkers between metal nodes, applied in photocatalysis, sensing, and biomedical therapy.
Porphyritic texture
Porphyritic texture is an igneous rock texture in which large crystals, called phenocrysts, sit in a distinctly finer-grained groundmass, classically formed by two stages of cooling.
Porphyry (geology)
Porphyry is an igneous rock containing large crystals, called phenocrysts, set in a distinctly finer-grained groundmass; the name also denotes the purple imperial stone of Roman Egypt.
Porphyry copper deposit
A porphyry copper deposit is a large, low-grade copper ore body formed by hydrothermal fluids above shallow intrusions, supplying about 60 percent of world copper.
Porro prism
A Porro prism is a 45°–90°–45° reflecting prism that deviates light 180° and inverts the image, named after Ignazio Porro, whose 1854 patent covered the binocular design.
Portable X-ray fluorescence
Portable X-ray fluorescence (pXRF), also called hand-held XRF, is a non-destructive method in which a compact instrument directs X-rays at a sample to measure elemental concentrations on the spot, used in soil screening, mining, and archaeology.
Portland stone
Portland stone, formally the Portland Stone Formation, is a Jurassic limestone from the Isle of Portland, Dorset, quarried since Roman times for buildings like St Paul's Cathedral.
Portlandite
Portlandite is an IMA-approved calcium hydroxide mineral, Ca(OH)₂, first described naturally at Scawt Hill, Northern Ireland, in 1933; it makes up 15 to 25% of hydrated Portland cement paste.
Posaconazole
Posaconazole (brand name Noxafil) is a broad-spectrum triazole antifungal drug, approved in the US in 2006, used to prevent invasive fungal infections in immunocompromised patients and to treat invasive aspergillosis and other rare fungal diseases.
Pöschl–Teller potential
The Pöschl–Teller potential is a one-dimensional potential in quantum mechanics, introduced in 1933, for which the Schrödinger equation can be solved exactly in closed form.
Posidonia Shale
Posidonia Shale (Posidonienschiefer): early Toarcian (~183 Ma) black bituminous shale of NW Europe, major petroleum source rock and famous Holzmaden fossil Lagerstätte of the Toarcian anoxic event.
Posit arithmetic
Posit arithmetic is a format for representing and computing with real numbers, designed by John Gustafson and Isaac Yonemoto in 2017 as a drop-in replacement for IEEE 754 floating point.
Position and momentum bases
In quantum mechanics, the position and momentum bases are continuous families of idealized eigenstates |x⟩ and |p⟩, existing only as distributions and linked by Fourier-transform duality.
Position eigenstates and continuous bases
Position eigenstates are the generalized eigenvectors |x⟩ of the quantum-mechanical position operator, forming a continuous basis normalized with the Dirac delta and not normalizable within the Hilbert space.
Position operator
The position operator in quantum mechanics represents a particle's spatial location, acting as multiplication by the coordinate; its relativistic extension, the Newton–Wigner operator, is debated.
Position representation
The position representation is the description of a quantum state by its wavefunction, obtained by projecting the state vector onto the eigenstates of the position operator.
Position vector
A position vector, also called a location vector or radius vector, points from a coordinate system's origin to a given point, representing its location as a directed displacement.
Position–momentum Fourier duality
Position–momentum Fourier duality is the fact that a quantum particle's position-space and momentum-space wave functions are Fourier transforms of each other, so both describe the same state.
Position–momentum uncertainty relation
The position–momentum uncertainty relation states that a quantum particle's position and momentum spreads obey Δx·Δp ≥ ℏ/2, proved by Kennard in 1927 and underlying atomic stability.
Positional isomerism
Positional isomerism, also called regioisomerism, is a form of constitutional isomerism in which compounds share the same molecular formula and carbon skeleton but differ in the position of a substituent or functional group.
Positive and negative predictive values
Positive and negative predictive values (PPV and NPV), also called precision rate, are the probabilities that a test result correctly reflects whether a person has the condition tested for.